[alsa-devel] EPIPE and underruns

Jaroslav Kysela perex at perex.cz
Mon Oct 4 23:08:44 CEST 2010

On Mon, 4 Oct 2010, Andrew Bell wrote:

> On Mon, Oct 4, 2010 at 3:45 PM, Jaroslav Kysela <perex at perex.cz> wrote:
>> On Mon, 4 Oct 2010, Andrew Bell wrote:
>>> Hi,
>>> Can somebody explain precisely the circumstances leading to an EPIPE
>>> as the result of a pcm_snd_writei()?
>> Simply, the driver consumed all queued samples in the ring buffer.
>>> What buffer has been underrun that leads to this error?  Does
>>> providing more data to pcn_snd_writei() help alleviate the issue?
>> Yes, also the ring buffer size may be increased depending on the stream
>> parameter setup to prevent underruns.
> Is there some reason not to write all the data that you want played at
> once other than snd_pcm_writei() may block?
> Can you point out some code that detects this underrun condition (I've
> found a bunch of candidates, but they don't obviously scream "underrun
> here!".

snd_pcm_update_state() in pcm_lib.c (driver) the 'if (avail >= 
runtime->stop_threshold)' condition.


Jaroslav Kysela <perex at perex.cz>
Linux Kernel Sound Maintainer
ALSA Project, Red Hat, Inc.

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